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Month: October 2012

An increasing number of energy efficient appliances operate on direct current (DC) internally, offering the potential to use DC from renewable energy systems directly and avoiding the losses inherent in converting power to alternating current (AC) and back. This paper investigates that potential for net-metered residences with on-site photovoltaics (PV) by modeling the net power draw of the ‘direct-DC house’ with respect to today’s typical configuration, assuming identical DC-internal loads. Power draws were modeled for houses in 14 U.S. cities, using hourly, simulated PV-system output and residential loads. The latter were adjusted to reflect a 33% load reduction, representative of the most efficient DC-internal technology, based on an analysis of 32 electricity end-uses. The model tested the effect of climate, electric vehicle (EV) loads, electricity storage, and load shifting on electricity savings; a sensitivity analysis was conducted to determine how future changes in the efficiencies of power system components might affect savings potential. Based on this work, we estimate that net-metered PV residences could save 5% of their total electricity load for houses without storage and 14% for houses with storage. Based on residential PV penetration projections for year 2035 obtained from the National Energy Modeling System (2.7% for the reference case and 11.2% for the extended policy case), direct-DC could save the nation 10 trillion Btu (without storage) or 40 trillion Btu (with storage). Shifting the cooling load by two hours earlier in the day (pre-cooling) has negligible benefits for energy savings. Direct-DC provides no energy savings benefits for EV charging, to the extent that charging occurs at night. However, if charging occurred during the day, for example with employees charging while at work, the benefits would be large. Direct-DC energy savings are sensitive to power system and appliance conversion efficiencies but are not significantly influenced by climate. While direct-DC for residential applications will most likely arise as a spin-off of developments in the commercial sector—because of lower barriers to market entry and larger energy benefits resulting from the higher coincidence between load and insolation—this paper demonstrates that there are substantial benefits in the residential sector as well. Among residential applications, space cooling derives the largest energy savings from being delivered by a direct-DC system. It is the largest load for the average residence on a national basis and is particularly so in high-load regions. It is also the load with highest solar coincidence.

At a time when India and other nations are grappling with myriad energy-related challenges, including unstable, costly power sources and growing greenhouse gas emissions, energy efficiency offers an alternative at a fraction of the cost of other new sources of energy. A consortium of leading Indian regulators, nongovernmental organizations, and international experts has recognized this opportunity and is working to develop effective policies that will bring significant domestic benefits to India while accelerating the global transition to energy efficiency.

Carbon dioxide (CO2) released into the oceans as a result of water pollution by nutrients — a major source of this greenhouse gas that gets little public attention — is enhancing the unwanted changes in ocean acidity due to atmospheric increases in CO2. The changes may already be impacting commercial fish and shellfish populations, according to new data and model predictions published in ACS’s journal, Environmental Science & Technology.

The biobased world’s traditional focus on producing fuels for cars, trucks and aircraft is quietly undergoing a major transition this summer toward production of chemicals needed for manufacture of hundreds of different consumer products, according to an article in the current edition of Chemical & Engineering News (C&EN). The cover story appears in the weekly newsmagazine of the American Chemical Society, the world’s largest scientific society.

The search for a “greener” way to prevent corrosion on the kind of aluminum used in jetliners, cars and other products has led scientists to an unlikely source, according to a report in ACS’ journal Industrial & Engineering Chemistry Research. It’s the juice of the date palm — those tall, majestic trees that, until now, were noted mainly as sources of food and traditional medicines.

Pet owners share their homes, their exercise habits and sometimes even their food with their four-legged companions. And increasingly, they are sharing the same diseases: Dogs and cats suffer from obesity, diabetes, heart disease, cancer, thyroid disorders and asthma, just like humans. Now researchers are examining the role that pollutants and other environmental factors may play in these dual diseases. Doctors and veterinarians have begun to work together to investigate common risk factors, such as pesticides, air pollutants, cigarette smoke and household chemicals.